1. Field of the Invention
One embodiment of the present invention relates to semiconductor devices and display devices.
2. Description of the Related Art
The increase in size of display devices such as liquid crystal display devices and EL display devices promotes the development of display devices with higher added value. In particular, techniques by which a driver circuit in a display device is composed of only transistors having the same conductivity type have been actively developed (see Patent Document 1 and Non-Patent Document 1).
FIG. 17A illustrates a driver circuit disclosed in Patent Document 1. The driver circuit disclosed in Patent Document 1 is composed of transistors M1, M2, M3, and M4. When a signal IN is at high level, the transistor M1 is turned off and the transistors M2 to M4 are turned on. Thus, a signal OUT exists in high level. On the other hand, when the signal IN is at low level, the transistor M1 is turned on, the transistors M2 and M4 are turned off, and the transistor M3 is temporarily turned on and then turned off. Thus, the signal OUT is at low level.
FIG. 17B illustrates a driver circuit disclosed in Non-Patent Document 1. The driver circuit disclosed in Non-Patent Document 1 is composed of transistors M11 to M19 and a capacitor C11. When a signal IN is at high level, the transistors M12, M14, M16, and M17 are turned on; the transistors M11, M13, and M15 are turned off; and the transistors M18 and M19 are temporarily turned on and then turned off. Thus, a signal OUT becomes low. On the other hand, when the signal IN is at low level, the transistors M12, M14, M16, M17, and M18 are turned off; the transistors M11, M15, and M19 are turned on; and the transistor M13 is temporarily turned on and then turned off. Thus, the signal OUT is set at high level.